Propagation Of Strong Shock Wave Research Articles

Lie group of invariance technique for analyzing propagation of strong shock wave in a rotating non‐ideal gas with azimuthal magnetic field

In this manuscript, the propagation of strong shock wave in a non‐ideal gas in the presence of azimuthal magnetic field with rotational effect is examined by using the Lie group of invariance technique with an assumption of uniform density in the undisturbed medium, whereas the azimuthal component of the fluid velocity and magnetic field are supposed to vary. The main advantage of this method is to reduce the number of independent variables by one. We obtained a special class of self‐similar solutions to the problem, and the flow profiles are depicted graphically behind the shock followed by a brief discussion on the behavior of solutions through graphs. The effects of variation in non‐ideal parameter, adiabatic index of the gas, Alfven–Mach number and ambient azimuthal velocity exponent on the flow variables are presented. All numerical calculations have been done using the “Mathematica”software.

Strong Shock in the Uniformly Expanding Universe with a Spherical Void

Propagation of strong shock wave in the expanding universe is studied using approximate analytic, and exact numerical solution of self-similar equations. Both solutions have similar properties, which change qualitatively, depending on the adiabatic powers $\gamma$. In the interval $1<\gamma<\gamma_{cr} \sim 1.16$ analytic and numeric solutions fill all the space without any voids and they are rather close to each other. At larger $\gamma>\gamma_{cr}$ a pressure becomes zero at finite radius, and a spherical void appears around the origin in both solutions. All matter is collected in thin layer behind the shock wave front. The structure of this layer qualitatively depends on $\gamma$. At the inner edge of the layer the pressure is always zero, but the density on this edge is jumping from zero to infinity at $\gamma \approx 1.4$ in both solutions.

Experimental and analytical evaluation of the acoustic radiation of femtosecond laser plasma filament sound sources in air.

Plasma filaments in air induced by femtosecond laser pulses lead to the generation of strong shock waves. This letter presents a systematic study, both experimental and theoretical, of the acoustic radiation by femtosecond laser-generated filaments. A theoretical model is developed based on the experimental results and is used to evaluate the directivity of the filament's acoustic radiation within and beyond the audible frequency range. It is shown that the acoustic directivity of plasma filaments can be derived from the model of a weighted acoustic line source, consisting of elementary point sources with N-shaped excitation.

Propagation of strong shock waves in a non-ideal gas

We studied the problem of converging cylindrical and spherical strong shock waves collapsing at the axis/center of symmetry for a non-ideal gas with constant density. We have applied the perturbation series technique which provides us a global solution to the implosion shock wave problem yielding the results of Guderley's local self-similar solution, which is valid only in the vicinity of the axis/center of implosion. We analyzed the flow parameters by expanding the solution in powers of time and found the similarity exponents as well as the corresponding amplitudes in the vicinity of the shock-collapse. The flow parameters and the shock trajectory have been drawn in the region extending from the piston to the center of collapse for different values of adiabatic coefficient and the non-ideal parameter.

The preplasma effect on the properties of the shock wave driven by a fast electron beam

Strong shock wave generation by a mono-energetic fast electron beam in a plasma with an increasing density profile is studied theoretically. The proposed analytical model describes the shock wave characteristics for a homogeneous plasma preceded by a low density precursor. The shock pressure and the time of shock formation depend on the ratio of the electron stopping length to the preplasma areal density and on the initial energy of injected electrons. The conclusions of theoretical model are confirmed in numerical simulations.

The LICPA-driven collider—a novel efficient tool for the production of ultra-high pressures in condensed media

Generation of strong shock waves for the production of Mbar or Gbar pressures is a topic of high relevance for contemporary research in various domains, including inertial confinement fusion, laboratory astrophysics, planetology and material science. The pressures in the multi-Mbar range can be produced by the shocks generated using chemical explosions, light-gas guns, Z-pinch machines or lasers. Higher pressures, in the sub-Gbar or Gbar range are attainable only with nuclear explosions or laser-based methods. Unfortunately, due to the low efficiency of energy conversion from a laser to the shock (below a few percent), multi-kJ, multi-beam lasers are needed to produce such pressures with these methods. Here, we propose and investigate a novel scheme for generating high-pressure shocks which is much more efficient than the laser-based schemes known so far. In the proposed scheme, the shock is generated in a dense target by the impact of a fast projectile driven by the laser-induced cavity pressure acceleration (LICPA) mechanism. Using two-dimensional hydrodynamic simulations and the measurements performed at the kilojoule PALS laser facility it is shown that in the LICPA-driven collider the laser-to-shock energy conversion efficiency can reach a very high value ∼ 15–20 % and, as a result, the shock pressure ∼ 0.5–1 Gbar can be produced using lasers of energy ⩽ 0.5 kJ. On the other hand, the pressures in the multi-Mbar range could be produced in this collider with low-energy (∼ 10 J) lasers available on the market. It would open up the possibility of conducting research in high energy-density science also in small, university-class laboratories.

An electromagnetic railgun accelerator: a generator of strong shock waves in channels

Processes that accompany the generation of strong shock waves during the acceleration of a free plasma piston (PP) in the electromagnetic railgun channel have been experimentally studied. The formation of shock waves in the railgun channel and the motion of a shock-wave-compressed layer proceed (in contrast to the case of a classical shock tube) in a rather strong electric field (up to 300 V/cm). The experiments were performed at the initial gas pressures in the channel ranging from 25 to 500 Torr. At 25 Torr, the shock-wave Mach numbers reached 32 in argon and 16 in helium. At high concentrations of charged particles behind the shock wave, the electric field causes the passage of a part of the discharge current through the volume of the shock-wave-compressed layer, which induces intense glow comparable with that of the PP glow.

The Propagation of Strong Shock Waves in Magnetohydrodynamics

In this paper, we have studied non-self-similar gas motions in presence of magnetic field which result from the propagation of plane, cylindrical and spherical shock waves through the gas requires complicated and cumbersome calculations. An approximate method of calculation of such motions is taken from

Gasdynamic modeling of strong shock wave generation from lightning in Titan’s troposphere.

In an effort to predict the characteristics of thunder on Titan, a model is being developed for the formation of the initial strong shock wave by a short cylindrical lightning discharge “segment.” (Such small discharge segments are later used to synthesize a tortuous cloud-to-ground 20 Km-long lightning channel in Titan’s troposphere.) The shock wave is obtained numerically as a solution of the coupled gasdynamic equations of state and conservation of momentum, mass, and energy. The relevant acoustic quantities are the pressure, density, particle velocity, and specific internal energy of the shock wave immediately following the discharge. Different scenarios for the initial deposition of energy from the discharge into the shock wave are investigated. The altitude-dependent ambient conditions in Titan’s lower atmosphere—temperature, pressure, and density—are extracted from Cassini-Huygens data, while specific heats and transport coefficients of the main constituents of Titan’s troposphere (N2, CH4) are obtained from the NIST Chemistry WebBook and interpolated at each altitude. The CH4 molar fraction, measured by the mass spectrometer onboard Huygens, varies from 0.0492 at 5 m to 0.0162 at 35 km (the latter marking the lower end of Titan’s tropopause). These parameters are used as inputs to the model for a complete thermodynamic characterization along the length of the lightning channel. [The work was funded by the Louisiana Space Consortium (LaSpace) and NASA.]

Burnett-Cattaneo continuum theory for shock waves

We model strong shock-wave propagation, both in the ideal gas and in the dense Lennard-Jones fluid, using a refinement of earlier work, which accounts for the cold compression in the early stages of the shock rise by a nonlinear, Burnett-like, strain-rate dependence of the thermal conductivity, and relaxation of kinetic-temperature components on the hot, compressed side of the shock front. The relaxation of the disequilibrium among the three components of the kinetic temperature, namely, the difference between the component in the direction of a planar shock wave and those in the transverse directions, particularly in the region near the shock front, is accomplished at a much more quantitative level by a rigorous application of the Cattaneo-Maxwell relaxation equation to a reference solution, namely, the steady shock-wave solution of linear Navier-Stokes-Fourier theory, along with the nonlinear Burnett heat-flux term. Our new continuum theory is in nearly quantitative agreement with nonequilibrium molecular-dynamics simulations under strong shock-wave conditions, using relaxation parameters obtained from the reference solution.

A diffusive-hyperbolic model for heat conduction

The present paper faces the problem of heat conduction within the framework of thermodynamics with internal state variables. A model, in which the heat flux vector depends both on the gradient of the absolute temperature and the gradient of a scalar internal variable, is proposed. Such a model leads to a diffusive-hyperbolic system which in general is parabolic, but also allows to shift to the hyperbolic regime. In the hyperbolic case the propagation of weak discontinuity waves is investigated. The Rankine-Hugoniot and Lax conditions for the propagation of strong shock waves are analyzed as well.

Furnace geometry effects on plume dynamics in laser ablation for nanotube synthesis

Laser ablation (LA) has become a popular method for production of carbon nanotubes where formation of gaseous carbon plume and liberation of catalyst particles are caused by the laser pulse. The plume dynamics in laser ablation is somewhat similar to point explosion where a large amount of energy is liberated in a small volume. The aim of this study is to explore thermal dynamics of catalyst particles that is crucial for the formation of carbon nanotubes. The challenge of this case is to describe numerically the strong shock wave propagation and reflections in the working space of laser furnace and its effect on plume dynamics and temperature regime of catalyst particles. The proposed model includes a multi-species formulation for concentration of chemical components combined with the compressible Euler equations. An axisymmetric unsteady computational gas dynamic model of plume expansion into ambient gas has been developed. In the present work, the system of governing PDEs is solved numerically using the relaxing TVD scheme in generalized curvilinear coordinates. To obtain the thermal behavior of catalyst particles the Eulerian solver has been combined with Lagrangian tracking of catalyst particles. The developed software has been implemented and tested using the set of test cases described in the paper. Reflected shock waves interact with the plume and catalyst particles, heat them, and cause temperature oscillations. The contradictory requirements of sustained high temperature of catalyst particles and minimum of temperature oscillations are discussed using the series of representative working space shapes.

Effects of solar wind inhomogeneities on transit times of interplanetary shock waves

Long-term forecasting, greater than a few hours, of geomagnetic activity requires reasonably accurate estimates of the arrival times of interplanetary shock waves of solar origin. The shock waves travel through an inhomogeneous interplanetary medium. Two major sources of uncertainty in estimates of arrival times are the variations of the velocity and the density of the ambient medium. The theory of propagation of strong shock waves through inhomogeneous media relates errors of estimate of shock arrival time to the inhomogeneities and shows that increases in the velocity along the Sun–Earth line lead to decreases in transit time and increases in the density lead to increases in transit time. The uncertainties in arrival time in both cases are proportional, in the linear approximation underlying the theory, to the perturbations or uncertainties in the velocity and density. The theory is applied to shock propagation through corotating inhomogeneities and used to calculate variances of arrival times using solar wind data. Four cases with different heliocentric radial dependences of density perturbation and fiducial shock speeds are considered. Numerical results based on NSSDC OMNI data give a variance of about 12– 24 h for a fiducial transit time of 48 h , depending on the model for the inhomogeneities. In the most plausible model, in which the density inhomogeneities δ ρ/ ρ increase linearly with heliocentric radius and the fiducial shock speed is proportional to the inverse square root of the radius, the ratio of variance to transit time is about 0.25, independent of fiducial transit time. The results are in general agreement with observations, suggesting that much of the variance of observed transit times results from the influence of interplanetary inhomogeneities.

Simulations of Compressible Flows with Strong Shocks by an Adaptive Lattice Boltzmann Model

An adaptive lattice Boltzmann model for compressible flows is presented. The particle-velocity set is so large that the mean flow may have a high velocity. The support set of the equilibrium-distribution function is quite small and varies with the mean velocity and internal energy. The adaptive nature of this support set permits the mean flows to have high Mach number, meanwhile, it makes the model simple and practicable. The model is suitable for perfect gases with an arbitrary specific heat ratio. Navier–Stokes equations are derived by the Chapman–Enskog method from the BGK Boltzmann equation. When the viscous terms and the diffusion terms are considered as a discretion error this system becomes an inviscid Euler system. Several simulations of flows with strong shocks, including the forward-facing step test, double Mach reflection test, and a strong shock of Mach number 5.09 diffracting around a corner, were carried out on hexagonal lattices, showing the model's capability of simulating the propagation of strong shock waves.

Superdense State of Metals Compressed by Shock Waves.

The paper presents explosive devices designs for generation of strong shock waves. Record values of specific internal energy of shock-compressed iron are obtained with use of them.

SHOCK WAVES, TURBULENCE AND LINE BROADENING PHENOMENA IN RR LYRAE

Recent results based on high resolution spectral observations of RR Lyrae are presented. They mainly concern the effects of the propagation of strong shock waves in the atmosphere.

Shock-wave propagation in elastoplastic shells, porous and reacting media

A mathematical model is built for the basics of mutually penetrating continua, allowing description of the propagation of strong shock waves in porous media, in the elastoplastic approximation. A concrete example compares experimental with lamellar model data.

Strong Shock Wave Propagation in a Mixture of a Gas and Dusty Particles with Gravitational Force

AbstractWhen a dusty comet collides with a planet, strong shock waves are produced in the dusty gas of the coma. In this case, the gravitational force plays an important role. With gravitational force, similarity solutions [1] of the strong shock wave propagation does not exist. In this paper, we study the effect of the gravitational force in a dusty gas by perturbation theory for the case of large Froude number. Numerical solutions are presented on the velocity, density and pressure distributions behind the shock as well as the shock speeds and its location with time under various conditions. The gravitational force does have predominant influence on the flow fields of the strong shock propagation in a dusty gas.

Similarity solutions of a strong shock wave propagation in a mixture of a gas and dusty particles

The similarity solutions of a strong shock wave propagation in a mixture of a gas and small solid particles have been investigated. Similarity solution exists only when the shock is very strong and the surrounding medium is of a constant density and at rest and with negligible counterpressure. The non-dimensional fundamental equations are derived and studied. The results depend on three non-dimensional parameters; i.e. (i) the ratio of the specific heats of the gas γ, (ii) the mass concentration of the solid particles k p in the mixture and (iii) the ratio of the density of the solid to that of initial density of the gas G. Numerical solutions for various values of γ k p and G are presented and discussed. The speeds of the shock wave front and its location with various energy releases are given.

Generation of strong shock waves in the high-speed pressing of metal powders

Generation of strong shock waves in the high-speed pressing of metal powders